Poorly Differentiated Chordoma with Rhabdoid Features

Abstract

Abstract Casestudy: Chordoma is an uncommon primary malignant tumor of the bone showing notochordal differentiation. The current World Health Organization classifies chordoma into three subtypes: conventional, chondroid, and dedifferentiated. Poorly differentiated chordoma (PDC) is a newly described variant of chordoma, with its own distinct features in terms of age distribution (common in pediatric and young adults), histopathology (lack of physaliphorous cells and chondromyxoid matrix), immunohistochemical and molecular characteristics (loss of SMARCB1/INI1 expression) and clinical outcome (poor prognosis with rapid onset of local recurrence and metastasis). Herein, we report the case of a 43 year old man with history of fall and injury of tailbone 2 years prior, who presented with pain and swelling at the sacrcoccygeal region and intermittent numbness in the legs. MRI of the pelvis showed a 9.8 cm lobulated mass centered on the sacrum with osseous destruction of S5 through coccyx, with intralesional hemorrhage, and mild heterogeneous enhancement. Biopsy of the sacrococcygeal mass demonstrated a malignant neoplasm composed of lobules of epithelioid cells with abundant eosinophilic cytoplasm showing focal vacuolization, and mild to moderate nuclear pleomorphism with an average 3 mitoses per high power field (400x). Immunohistochemically, the neoplastic cells were positive for pancytokeratin, CAM 5.2, vimentin and brachyury. They had loss of SMARCB1 (INI1) and were negative for S100, CK7, CK20, desmin and actin. The location, imaging studies, morphologic features and immunohistochemical profile were consistent with poorly differentiated chordoma with rhabdoid features. With its specific clinical, morphologic, immunophenotypical, and molecular features, PDC may be recognized as a chordoma subtype in a future WHO classification. According to current knowledge, the diagnosis of PDC should be restricted to cases with brachyury expression (specific for notochord tumors) and INI1 protein loss, especially in tumors of pediatric and young patients, regardless of cellular characteristics.